Most consumers have come to expect scented laundry products and to expect that fabrics which have been laundered to also have a pleasing fragrance. It is also desired by consumers for laundered fabrics to maintain the pleasing fragrance over time. Perfume additives make laundry compositions more aesthetically pleasing to the consumer, and in some cases the perfume imparts a pleasant fragrance to fabrics treated therewith. However, the amount of perfume carry-over from an aqueous laundry bath onto fabrics is often marginal and does not last long on the fabric. Fragrance materials are often very costly and their inefficient use in rinse added fabric softener compositions and ineffective delivery to fabrics from the rinse results in a very high cost to both consumers and fabric softener manufacturers. Industry, therefore, continues to seek with urgency for more efficient and effective fragrance delivery in fabric softener products, especially for improvement in the provision of long-lasting fragrance to the rinsed fabrics.
Carrier mechanisms for perfume delivery, such as by encapsulation, have been taught in the prior art. See for example, U.S. Pat. No. 5,188,753.
U.S. Pat. No. 5,378,468, Suffis et al, issued Jan. 3, 1995 describes specific types of personal care compositions, such as deodorant sticks, comprising assertedly "body-activated" fragrances. The term apparently refers to the previously known tendency of materials such as acetals and ketals derived from fragrance alcohols to hydrolyze under acidic pH conditions thereby releasing fragrance. See, for example, U.S. Pat. No. 3,932,520, Hoffman, issued Jan. 13, 1976.
See also, Steffen Arctander, "Perfume and Flavor Chemicals", Arctander, N.J., 1969. Factors affecting substantivity of fragrance materials on fabrics are discussed in Estcher et al. JAOCS 71 p. 31-40 (1994).
The selected potential fragrance materials described by Suffis et al include particular acetals and ketals, exemplified by propylene glycol vanillin acetal. The materials exemplified apparently are rather hydrophilic short chain alcohol or diol derivatives of fragrance aldehydes and ketones that upon hydrolysis, deliver one mole of the aldehyde per mole of the potential fragrance material. The present inventors believe that short chain hydrophilic acetal and ketal materials are incompatible with acidic rinse added fabric softening compositions as described hereinafter. The Suffis et al development is designed to be incorporated with a personal care product vehicle, resulting in clear deodorant sticks and the like.
For rinse added fabric softening use, it is important that rather hydrophobic pro-fragrant compounds be used in order to enhance deposition onto surfaces in the wash solution and retention on the washed surface during rinsing. In Suffis et al, the compositions containing the potential fragrance materials are applied directly to the substrate (i.e. skin); therefore, the deposition problems resulting from dilution, rinsing, etc. are not at issue.
Esters of perfume alcohols are known in the art for providing extended delivery of fragrances in fabric softening compositions. See, for example, U.S. Pat. No. 5,531,910, Severns, issued Jul. 2, 1996. However, the manufacture of pro-fragrant esters known in the art can present costly and significant synthetic challenges. Derivitization of tertiary fragrance alcohols into simple esters is particularly difficult, often resulting in low yields and increased levels of less desirable side products. Therefore, industry continues to seek improved alternatives for generating pro-fragrances through economic and effective means.
It has now surprisingly been discovered that these problems can unexpectedly be overcome by the use of .beta.-keto-esters as pro-fragrances. The hydrophobic .beta.-keto-esters of the present invention demonstrate improved substantivity through the rinse. These ingredients further provide sustained gradual release of fragrance raw materials, especially fragrance raw material alcohols and ketones, from laundry items over an extended period of time. The use of .beta.-ketoesters also provides an alternative synthetic route to derivatize fragrance raw material alcohols into pro-fragrance compounds. This method is particularly well suited to derivatization of tertiary alcohols. Tertiary alcohols can be derivatized with higher yields and improved purity via this method.